On the one hand, towed bodies of this type are used in the military sector, where they are used for training purposes as targets or for aircraft deflection. On the other hand, towed bodies are also used in the civil sector for a variety of measurement purposes. As a general rule, there are very limited possibilities for contactless remote sensing with a powered aircraft, usually an airplane or a helicopter, in the atmospheric boundary layer up to an altitude of 300 m due to naturally occurring and artificial obstacles. In good visibility conditions (no low cloud, or no clouds at all), measurements can be performed with the airplane at an altitude of 60 m, whereas under poor visibility conditions (deep cloud, fog, rain, etc.), they can only be performed at a maximum altitude of 300 m, in other words only at the edge of the atmospheric boundary layer. High safety requirements for flight operation are imposed at altitudes of less than 150 m. However, it is often of particular interest to perform measurements immediately above the ground, for example directly over the surface of sea ice or beneath a cloud layer without any direct visual contact with the aircraft. Unmanned towed bodies are used for this purpose, which do not have their own drive systems (unlike drones), but are towed through the air by the aircraft, which flies in a non-critical altitude range in excess of 300 m in such cases. The general flight direction of the towed body is thus determined by the aircraft. In this case the towed body is connected to the aircraft via a towing cable of variable length. A distinction should be made between passive towed bodies, which do not possess any independent maneuverability, and active towed bodies, which do possess independent maneuverability in airspace—within the scope of the general flight direction determined by the aircraft.
Towed bodies for measurement purposes are used in the polar regions, for example, to obtain information about the surface of sea ice and the thickness distribution of said sea ice. However, atmospheric measurements may also be performed with such towed bodies (for example, measurements of the content of BC (black carbon), aerosol measurements (particle concentrations, chemical composition) and atmospheric trace gas measurements (CO, CO2, SO2, NOx) to obtain information about meteorological conditions and the properties of clouds, geophysical prospecting and environmental observations (emissions from ships and power plants and detection of land mines) in accessible residential or industrial areas, but also particularly inaccessible areas (polar regions, oceans, mountains, rainforests, deserts)). Measurements may take place at one altitude (towed body flight altitude) or at two altitudes synchronously (aircraft and towed body flight altitudes) inside or both inside and outside the planetary boundary layer. Furthermore, vertical measurement profiles at different flight altitudes down to just above the ground can be recorded in good visibility conditions by using a maneuverable towed body without having to change the length of the towing cable.
An active towed body for measurement purposes is known in the art from the presentation entitled “Measurements of Air-Sea Fluxes with a Controlled Towed Vehicle (CTV)” by D. Khelif et al. The presentation was published at the Ocean Sciences Meetings of the UNOLS Scientific Committee for Oceanographic Aircraft Research during the Town Hall Session in Portland, Oreg., USA, on Feb. 22, 2010 and can be downloaded online (as at Nov. 19, 2014) via the following link: <<http://www.unols.org/sites/defaultifiles/201002scoap_09.pdf>>. The CTV in the prior art relates to a partially active towed body for wireless determination of measurement data from the airspace. The towed body has a variety of sensors for determining measurement data, for example meteorological sensors (pressure and temperature sensor, hygrometer and anemometer, and sensor technology for trace gas measurements) and for determining its position in the air, for example radar-assisted altimeters, GPS system, navigation system and video camera. The towed body has two short wings, which can be rotated around a radial axis and are used to change the height of the towed body in flight. The towed body from the prior art is cylindrical and thus has an unfavorable aerodynamic design. For flight stabilization purposes, the towed body from the prior art therefore comprises a plurality of rigid wind deflectors. Furthermore, the towed body from the prior art has a computer-assisted control device which comprises an automatic flight control system for independent control of the vertical flight position (flight altitude) of the towed body. By exclusively changing the flight altitude, it is possible to fly over obstacles under control, but this must be controlled by an operator on board the towing aircraft. If a maneuvered overflight is not possible, the towed body is taken in or jettisoned, although this poses a considerable environmental hazard and generally leads to the destruction of the towed body.
GB 737318 A describes an active towed body as an aerial target for military purposes, which can be towed through the air by an aircraft by a towing cable. The towed body is designed to be aerodynamic and comprises a curved fuselage both in the vertical and in the horizontal longitudinal plane (in which the longitudinal axis x is located). This leads to a torpedo-shaped, rotationally symmetrical fuselage. The towed body also comprises two wings and a tail fin on its tail. In this case, the wings are designed to be delta-shaped when viewed from above and run completely flat in terms of their cross section. The wings are arranged at right angles to the fuselage and halfway up the fuselage (in towing mode they are therefore aligned horizontally during straight flight). When viewed from above, the wings are arranged in the rear section of the fuselage. The towed body from the prior art is active, i.e. designed such that it can be maneuvered and can be steered in all three spatial directions. In addition, the wings comprise rotatable wing tips (corresponding to ailerons), by means of which a curve inclination of the towed body can be achieved. Elevators are also integrated in the wings and a rudder is integrated in the tail fin. All rudders are controlled by a control device which is arranged in a unit chamber in the fuselage. The control device is operated manually from the aircraft, remote controlled by a base station or by autopilot from the towed body, said autopilot serving to stabilize the position of the towed body in towing mode. Furthermore, the power supply for the towed body is located in the unit chamber in the form of accumulators. The unit chamber of the towed body from the prior art is manufactured from solid material and comprises corresponding recesses for the control device and the power supply. The fuselage also comprises a load chamber, which is completely filled by a parachute. The towing cable is attached to a coupling on a jettisonable nose section of the towed body. The towed body can be decoupled from the aircraft by jettisoning the nose section. The towed body has gliding properties due to its aerodynamic shape and can be landed with the aid of the parachute.
DE 424 378 A and DE 196 52 414 A1 also disclose means of bending the wings to stabilize an aircraft. In these cases, however, the wings are arranged on the side of or above the fuselage and are initially bent upwards. The displacement effect as a result of the air flowing upwards along the sides of the wings increases the stability of the aircraft, but also results in lower lift. U.S. Pat. No. 6,640,739 B2 discloses a device for remote underwater exploration, which is suspended beneath an aircraft as a load for transportation purposes, said device being designed aerodynamically in such a way that it glides downwards after decoupling from the aircraft, supported by a parachute in this process, and lands intact on the water in which it is then submerged. In this case, however, the exploration device has a simple cylindrical form and two straight wings placed on its upper face. US 2002/0190162 A1 discloses a towed body for measurement purposes, said towed body comprising a fuselage which is curved in its horizontal and vertical longitudinal planes. In this case, however, the towed body is designed to be passive and does not have any independent maneuverability. The towed body known in the art from U.S. Pat. No. 6,765,383 B1 for measurement purposes is also passive and is designed with a double curved fuselage and has a nose boom in which various measuring instruments or their sensors are arranged. DE 199 16 145 A1 discloses a system in which the aerofoils of an aircraft for increasing lift and stabilizing flight behavior are each composed of a plurality of segments. In this case, however, it relates to flow chambers which are open at the bottom and with a narrowing cross-section.
The earlier patent application DE 10 2014 001 873 A1 is also concerned with a maneuverable, active towed body for scientific and commercial measurement purposes and is based on the CTV described above. In contrast, in the towed body described in the earlier application, full maneuverability is achieved in the entire airspace. Automated, independent circumnavigation of detected obstacles already represents a relevant safety aspect in the towed body claimed in the earlier application, taking the pressure off the aircraft pilot to a significant extent. However, in the earlier application, the emphasis is not on the aerodynamic design of the towed body with optimized load holding, but on the ability to reliably switch the towed body to a neutral flight position by means of an electromechanical malfunction module in the event of a fault or failure of the control electronics so that it can be safely recovered by the aircraft. The present invention relates to different aspects to the earlier application, but DE 10 2014 001 873 A1 is hereby incorporated by reference with regard to other general matters.